On 8/19/21 6:27 AM, Mike Rapoport wrote: > Such PMDs are created when free_kernel_image_pages() frees regions larger > than 2Mb. In this case a part of the freed memory is mapped with PMDs and > the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will > mark the PMD as not present rather than wipe it completely. > > Make kern_addr_valid() to check whether higher level page table entries are > present before trying to dereference them to fix this issue and to avoid > similar issues in the future. > > Reported-by: Jiri Olsa <jolsa@xxxxxxxxxx> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> # 4.4... > pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > + if (!pmd_present(*pmd)) > return 0; Yeah, that seems like the right fix. The one kern_addr_valid() user is going to touch the memory so it *better* be present. p*d_none() was definitely the wrong check. Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx>
